Smallpox A013

Current RMA Instruments

Changes from previous Instruments

ICD Coding:

• ICD-10-AM Codes: B03

Brief description

Smallpox is a serious clinical illness caused by infection with the variola virus, a member of the Orthopoxvirus genus. Two strains- variola major and variola minor- can cause the disease, with variola major responsible for the ordinary and more severe form. Smallpox has been eradicated worldwide, with the last naturally occurring case reported in 1977. Currently, variola virus is retained only in two authorised high-security laboratories in the United States and Russia. 

Confirming the diagnosis

A diagnosis of smallpox should only be considered if the disease re-emerges through accidental laboratory exposure or an act of bio-terrorism. The SOP requires laboratory confirmation of infection with variola virus, regardless of the clinical presentation. Clinical features- typically acute onset of fever, prostration, headache, body aches, followed by a characteristic vesicular or pustular rash- must be accompanied by definitive laboratory testing specific for variola virus. 

Additional diagnoses covered by SOP

• Smallpox caused by variola major or mariola minor
• Ordinary type smallpox, modified type or haemorrhagic type smallpox (caused by variola virus are clinical variants of the same disease)

Conditions not covered by these SOPs   

• Monkeypox (mpox) # - caused by monkeypox virus, a different orthopoxvirus
• Cowpox #

* another SOP applies  - the SOP has the same name unless otherwise specified

# non-SOP condition

Clinical onset

The clinical onset refers to the earliest point in time, as identified by the treating doctor, when symptoms consistent with smallpox first appeared. Early features typically include sudden onset of high fever, severe malaise or prostration, headache, and muscle aches, followed within days by the development of a characteristic vesicular or pustular rash. These symptoms precede any laboratory confirmation. 

Clinical worsening

When considering possible clinical worsening, it is important to determine whether any deterioration exceeds what would normally be expected in the natural course of smallpox. Progression may involve increasing rash burden, development of pustules, systemic toxicity, or complications such as encephalopathy, secondary bacterial infection, or, in severe cases, haemorrhagic manifestations. True clinical worsening would be assessed in the context of appropriate medical management and public health response. The emergence of complications represents part of the recognised disease spectrum and does not indicate a separate condition unless a new, distinct illness develops (e.g. secondary bacterial pneumonia). Any suspected case would require assessment by an infectious diseases specialist.